DE102012201732B4 - Numerically controlled machine tool and method for controlling an automatic rotary alignment process of a gear on the machine tool - Google Patents

Abstract

Numerically controlled machine tool with at least 5 axes for machining a workpiece (200) clamped to a clamping means (130) of the machine tool (100) by means of a tool received on a work spindle (111) of the machine tool (100), comprising: a numerical machine control device (150) which is set up to control the tool received on the work spindle (111) of the machine tool (100) relative to the workpiece (200) clamped to the clamping means (130) of the machine tool (100) on the basis of numerical control data, wherein the machine control device (150) is further set up to control an automatic rotary alignment process for determining at least one rotary zero point shift for final machining of a gear (200) clamped to the clamping means (130), in which: - a measuring probe controlled by the machine control device (150) (140) with a plurality of tooth flanks (201a, 201b; 202a, 202b) of the gear (200) at a plurality of predetermined touch positions on each of the tooth flanks, the plurality of tooth flanks comprising a group of left tooth flanks (201a, 202a) and a group of right tooth flanks (201b, 202b),- the machine control device (150) compares the determined actual position with a respective predetermined target position for each of the predetermined touch positions and determines a target-actual deviation for each touch position on the basis of the comparison,- the machine control device (150) determines at least one rotary zero point shift for the final machining of the gear (200) clamped on the clamping means (130) on the basis of the determined target-actual deviations, and- the machine control device (150) is set up to determine the at least one rotary zero point shift of the gear (200) clamped on the clamping means (130) clamped gear (200) taking into account a predetermined minimum material removal depth, with the proviso that during final machining of the gear (200) at each touch position at least material is removed up to the predetermined minimum material removal depth, and if this is not possible, the machine control device (150) is set up to separately evaluate the target-actual deviations determined for the group of left tooth flanks (201a, 202a) and the target-actual deviations determined for the group of right tooth flanks (201b, 202b), and to determine a first zero point shift for the group of left tooth flanks (201a, 202a) and a second zero point shift for the group of right tooth flanks (201b, 202b).

Description

The present invention relates to a numerically controlled machine tool with at least 5 axes for machining, in particular milling, a gear clamped to a clamping means of the machine tool by means of a tool held on a work spindle of the machine tool. The machine tool comprises a numerical machine control device which is designed to control the tool held on the work spindle of the machine tool relative to the gear (e.g. spur gear, ring gear or bevel gear) clamped on the clamping means of the machine tool on the basis of numerical control data. In particular, the present invention relates to a functional extension of standard machine tools, such as milling machine tools, milling/drilling machine tools, universal machine tools and machining centers.

Background of the invention

From the EN 10 2009 008 124 A1 A method is known for producing gears such as spur gears, bevel gears and ring gears with any tooth shape (e.g. straight toothed, helical toothed, curved toothed or spiral toothed, etc.) and with any tooth profile (e.g. involute profile, cycloid profile, etc.) on numerically controlled CNC standard machine tools using standard milling tools.

In such a process, the gear is manufactured in several steps, whereby first a pre-milled gear is manufactured from a blank in a soft machining process on the standard CNC machine tool (in contrast to previous processes using special gear cutting machines) with a predetermined gear shape. After the soft machining, the pre-milled gear is removed from the machine tool and subjected to a material-hardening heat treatment to harden at least one surface layer of the pre-milled gear. After this heat treatment, the pre-milled, hardened gear is clamped again on the clamping device of the CNC standard 5-axis machine tool to undergo a final finishing or hard machining.

It is conventionally known that after clamping the pre-milled, hardened gear, before starting the final finishing or hard machining on the machine tool, a machine tool coordinate system must be aligned with the workpiece coordinate system of the clamped workpiece, since the numerical control data (e.g. one or more NC programs) for controlling the finishing or hard machining are created on the basis of the workpiece coordinate system and contain travel commands for linear and rotary axes of the machine tool that can only be implemented by the machine tool on the basis of the machine tool coordinate system. This is referred to as a so-called zero point shift, in which a deviation between the coordinate zero point of the machine tool coordinate system and the coordinate zero point of the workpiece coordinate system is determined, and this deviation is then taken into account numerically when processing the numerical control data for the finishing or hard machining.

In the case of rotationally symmetrical workpieces, such as pre-milled gears, in particular spur gears, bevel gears and also ring gears, it is particularly necessary to determine a rotary zero point shift after the workpiece has been clamped in place before the final machining begins. In the case of a machine tool in which the rotationally symmetrical workpiece is clamped on a rotary table, for example, which can be controlled by means of a rotary axis of the machine tool, it is particularly necessary to determine a rotary zero point shift between the zero point of the rotary axis controlling the rotary table and the rotary zero point of the clamped workpiece.

In such an alignment process, the pre-milled, hardened gear is usually first aligned translationally based on determining the position of the center hole and then aligned rotationally in a rotational alignment process based on a scanning process using a measuring probe on the machine tool or by determining the position of an off-center position hole on the face of the gear. The clamped and aligned gear can then be finished based on the determined zero point shifts, possibly translationally and rotationally. In the alignment method using a measuring probe, two opposing tooth flanks of a tooth or a tooth gap are each scanned once in order to determine a rotational alignment of the clamped gear.

If there is sufficient stock on the tooth flanks after soft machining, a sufficient hardening depth and a low thermal distortion after heat treatment, the alignment process described above is suitable for determining a rotary zero point offset. shift is usually sufficient, especially with smaller gears.

However, the new processes in which gears such as spur gears, bevel gears and ring gears with any tooth shape are manufactured on numerically controlled CNC standard 5-axis machine tools using standard milling tools make it possible to manufacture very large, sometimes custom-made gears with diameters of up to over a meter or more on large 5-axis machine tools or machining centers, where an unusually large thermal distortion can occur on the tooth flanks after heat treatment. The greatest thermal distortion usually occurs in the places that have the least accumulation of material and the greatest distance from the gear body, i.e. in the case of gears, this is usually at the tooth tip, so that the teeth are essentially bent. Opposite tooth flanks, i.e. left and right tooth flanks, can warp or deform completely differently as a result of the heat treatment and may even warp in different directions.

If very large gears in particular, such as those used for ship gears, are rotationally aligned using the conventional methods described above before finishing, the distortion of the tooth flanks or their deformation can be so great that the amount of material removed during finishing is too little at some points on the tooth flanks and there may even be points on the tooth flanks where no material is removed during finishing, so that the gear's rolling behavior may later be unfavorable. Furthermore, the distortion of the tooth flanks at other points on the tooth flanks can be so great that too much material is removed at these points. At these points, the hardening depth hardened during heat treatment may be exceeded when material is removed, and unfavorable soft or non-hardened points may therefore appear on the surface of the finished tooth flanks, which significantly reduces the gear's susceptibility to wear.

In view of the above-described problems of the alignment methods known from the prior art for determining a rotary zero point shift, it is an object of the present invention to provide an improved alignment process for soft-machined and heat-treated gears on a machine tool, in which the disadvantages described above can be avoided and in which the rotary zero point shift can still deliver advantageous results, particularly in the case of very large gears with diameters of up to over one meter, so that during finishing it can be avoided that points occur on tooth flanks where too much and/or too little material is removed.

EN 10 2009 008 121 A1 discloses a method for generating transformed control data for controlling a tool on a machine tool for machining a workpiece by cutting, whereby faulty machining can be avoided even if the workpiece is inaccurately clamped in the machine tool.

Furthermore, EN 10 2009 008 120 A1 a machine tool for the program-controlled machining of a workpiece by means of one or more tools controlled on the basis of control data by cutting, wherein the machine tool comprises at least 5 simultaneously controllable axes and furthermore a clamping means for clamping the workpiece and a control device with a receiving means for receiving one of the one or more tools of the machine tool, wherein in particular the control device of the machine tool is suitable for controlling the tool received in the receiving means on the basis of the control data along a tool path for removing material from the workpiece clamped in the clamping means.

DE 23 64 916 A1 discloses a test device with a probe for testing the flanks of gears using electronic means. The measured values are preferably fed as digital signals to a computer, which compares them with target values entered by a program according to the progress of the relative movement and determines the target-actual difference.

In addition, DE 43 36 267 A1 a method for measuring a profile of a workpiece with a probe tip of a probe.

Furthermore, EN 10 2008 007 127 A1 a method for measuring components in a Cartesian measuring machine or machine tool, which is suitable for determining the exact position of a component in a three-dimensional Cartesian coordinate system by setting up an implicit, overdetermined, nonlinear system of equations.

Summary of the invention

The problem is solved by the features of claims 1, 13 and 14. Special embodiment Forms of implementation are described in the dependent patent claims.

According to a first aspect of the invention, a numerically controlled machine tool with at least 5 axes for machining, in particular milling, a workpiece clamped to a clamping means of the machine tool by means of a tool held on a work spindle of the machine tool is proposed. The machine tool preferably comprises a numerical machine control device which is designed to control the tool held on the work spindle of the machine tool relative to the workpiece clamped to the clamping means of the machine tool on the basis of numerical control data.

According to the invention, the machine control device of the machine tool is designed to control an automatic rotary alignment process for the numerical determination of a rotary zero point shift for final machining of a gearwheel clamped to the clamping means. A "rotary zero point shift" is understood here to mean in particular a numerical value (preferably in particular an angle value) of a rotary axis rotation to be determined (in particular according to a rotary degree of freedom) which is required for the subsequent final machining in order to align a coordinate or angle zero point of the rotary axis(es) in the machine tool coordinate system with a rotary coordinate or angle zero point of the clamped gearwheel in the workpiece coordinate system, wherein the workpiece coordinate system is used as a basis when creating or generating numerical control data such as an NC program, but the rotary axis(es) are controlled by means of commands of the numerical control data such as an NC program with reference to the machine tool coordinate system.

In this automatic rotary alignment process, according to the invention, a measuring probe controlled by the machine control device determines or measures a respective actual position for a plurality of tooth flanks of the gear at a plurality of predetermined probe positions on each of the tooth flanks, the machine control device compares the determined actual position with a respective predetermined target position for each of the predetermined probe positions and determines or calculates a target-actual deviation for each probe position on the basis of the comparison, and the machine control device determines or calculates at least one rotary zero point shift for the final machining of the gear clamped to the clamping device on the basis of the determined target-actual deviations.

The invention is based on the basic idea that different points on the tooth flanks of the gear can distort differently across the tooth flank due to the heat treatment in the hardening process, and different tooth flanks can also distort differently across the gear. In order to be able to compensate for these distortion effects better by the rotary zero point shift to be determined, the rotary zero point shift is determined according to the invention by a plurality of target-actual position comparisons using a measuring probe on a plurality of tooth flanks in order to be able to compensate for the effects of the different distortions of different tooth flanks in an improved manner, and on each of these tooth flanks at a plurality of probe positions in order to be able to compensate for the effects of the different distortions at different points on the respective tooth flanks in an improved manner.

After determining the target-actual deviations at a plurality of probe positions, which according to the invention are arranged both on a plurality of tooth flanks of the gear and also on each of the tooth flanks at different locations, the plurality of determined target-actual deviations are evaluated to determine a rotary zero point shift.

When determining the rotary zero point shift according to the invention on the basis of a target-actual position comparison at a plurality of probe positions arranged on a plurality of tooth flanks of the gear and on each of these tooth flanks at a plurality of different positions, both the possibly different distortions occurring at different locations of a respective tooth flank and the possibly different distortions occurring on different tooth flanks can be compensated for in an improved manner.

Accordingly, the present invention makes it possible to determine a rotary zero point shift for the final machining of the gear, while simultaneously avoiding or at least significantly reducing both the occurrence of spots on tooth flanks with too much material removal and the possible resulting occurrence of soft spots on tooth flanks, which lead to increased susceptibility to wear of the gear, and the occurrence of spots on tooth flanks with too little or no material removal and the possible resulting occurrence of deteriorated rolling behavior of the gear.

For the determination of the rotary zero point shift, the rotary zero point shift can, for example, be determined or calculated in a simple manner according to a particularly useful example in such a way that in a simulation, by varying the rotary zero point shift, it is checked which rotary zero point shift is at least required to make all target-actual deviations greater than or equal to zero.

It should be noted that the values of the individual target-actual deviations can have both positive and negative values. Positive values according to a selected definition mean that the tooth flank is warped away from the tooth at the respective probe position, and negative values mean that the tooth flank is warped towards the tooth at the respective probe position. As soon as a rotary zero point shift can be determined with such a definition, in which all target-actual deviations are greater than or equal to zero, it is possible to set this determined rotary zero point shift and take this determined rotary zero point shift into account during the subsequent final machining at all probe positions in such a way that not too little material is removed.

In particular, it is possible, for example, to determine in a particularly simple manner which zero point shift is required to make the smallest of the determined target-actual deviations greater than or equal to zero, and to record this value as the determined rotational zero point shift.

Optionally to the above aspects, it is preferably also possible to additionally specify a minimum allowance, wherein the rotary zero point shift can then be determined in such a way that in a simulation, by varying the rotary zero point shift, it is checked which rotary zero point shift is at least required to make all target-actual deviations greater than or equal to the specified minimum allowance. In particular, it is preferably possible, for example, to determine in a particularly simple manner which zero point shift is required to make the smallest of the determined target-actual deviations greater than or equal to the specified allowance, and to record this value as the determined rotary zero point shift.

In the above-described embodiments for determining the rotary zero point shift, it must be taken into account that a rotary zero point shift with the above-mentioned definition of the signs of the target-actual deviations reduces the target-actual deviations on right flanks while increasing the target-actual deviations on left flanks, or increases the target-actual deviations on right flanks while reducing the target-actual deviations on left flanks. If it is not possible to adjust right and left tooth flanks using the same rotary zero point shift, further embodiments of the present invention provide for right and left flanks to be evaluated separately and separate rotary zero point shifts to be determined. This will be described in more detail later.

To determine the rotational zero point shift, the rotational zero point shift can be determined or calculated, for example, according to further expedient embodiments, as a fit value or best fit value by means of a mathematical adjustment calculation.

To determine a fit value or best fit value, a distance value can preferably be calculated on the basis of the determined target-actual deviations, whereby the distance value preferably represents a value describing the size of the total deviation taking into account all determined target-actual deviations. In the mathematical compensation process, this distance value is then automatically minimized, preferably by varying the rotary zero point shift, and the value of the rotary zero point shift with the distance value minimized then results in the determined rotary zero point shift for use in the subsequent final machining of the gear within the framework of this mathematical compensation calculation.

It should be noted that the values of the individual target-actual deviations can take on both positive and negative values. Preferably, positive values according to a selected definition mean that the tooth flank is warped away from the tooth at the respective contact position, and negative values preferably mean that the tooth flank is warped towards the tooth at the respective contact position. For this reason, the distance value as a function of the target-actual deviations should preferably be selected in such a way that it can be described as a function of the amounts of the target-actual deviations or preferably as a function of the squares of the target-actual deviations. Furthermore, the distance value as a function of the target-actual deviations should preferably be selected in such a way that the value of the distance value increases strictly monotonically with the amount or preferably with the square of each individual target-actual deviation. The distance value could expediently be a strictly monotonically increasing function of the sum of the amounts of all Target-actual deviations or preferably as a strictly monotonically increasing function of the sum of the squares of all target-actual deviations. When using mathematical compensation calculations, it is also preferred that a further additional check is carried out to determine whether positive values for the target-actual deviations can really be achieved at all probe positions after rotary zero point shifting in accordance with the value determined in the compensation calculation (or, according to further explanations, values greater than or equal to a specified allowance). If this is not the case, the value of the determined rotary zero point shift can be corrected accordingly (if necessary for left and right tooth flanks separately) until positive target-actual deviations or target-actual deviations greater than or equal to a specified allowance are achieved at all probe positions.

Preferably, the machine control device is further configured to automatically control the final machining of the clamped gear after the automatic alignment process on the basis of control data specified for the final machining, wherein the at least one determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the gear (in particular taken into account numerically).

According to this preferred embodiment, the final machining of the gear on the machine tool can be carried out much more efficiently and with greatly reduced downtime on the machine, since after the gear is clamped on the machine tool following the hardening heat treatment, an optimal rotary zero point shift can be determined immediately and automatically, which is then advantageously automatically taken into account in the final machining of the gear that starts immediately afterwards. Manual, controlling intervention by the operator after determining the rotary zero point shift and before starting the final machining on the machine tool is advantageously not required.

According to the invention, the plurality of tooth flanks comprise a group of left tooth flanks and a group of right tooth flanks, wherein the machine control device is configured to separately evaluate the target-actual deviations determined for the group of left tooth flanks and the target-actual deviations determined for the group of right tooth flanks.

Accordingly, the knowledge is used that all tooth flanks can warp differently due to the hardening heat treatment, whereby the differences in warping between two different left flanks or differences in warping between two different right flanks are typically smaller than differences in warping between a left flank and a right flank. With additional or alternative separate evaluation of the target-actual deviations of touch positions on left flanks and the target-actual deviations of touch positions on right flanks, it is thus possible to determine a first rotary zero point shift for left tooth flanks and a second rotary zero point shift for right tooth flanks in addition to or as an alternative to determining a single rotary zero point shift.

Preferably, the machine control device is further configured to determine a first rotary zero point shift for the group of left tooth flanks and a second rotary zero point shift for the group of right tooth flanks when separately evaluating the target-actual deviations determined for the group of left tooth flanks and the target-actual deviations determined for the group of right tooth flanks.

This has the advantage that the final machining of the gear can be further improved. If the determination of a single rotary zero point shift with a joint evaluation of the target-actual deviations of the left and right tooth flanks leads to a result in which, after final processing, there are areas with too much material removal and/or areas with too little or no material removal due to excessive and varying thermal distortion of the tooth flanks, this can be avoided by evaluating the left and right tooth flanks separately and determining the first zero point shift for the left tooth flanks and the second zero point shift for the right tooth flanks.

Preferably, in this case, the machine control device is configured to automatically control the final machining of the clamped gear after the automatic alignment process on the basis of control data specified for the final machining, wherein the first determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the left tooth flanks and the second determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the right tooth flanks.

As already mentioned above, by evaluating the left and right tooth flanks separately and determining the first zero point shift for the left tooth flanks and the second zero point shift for the right tooth flanks, it is possible to avoid areas with too much material removal and/or areas with too little or no material removal. The only effect that would occur if a first zero point shift were used for the final machining of the left flanks and a different second zero point shift for the final machining of the right flanks would be that the tooth thickness of the teeth of the finished gear would be reduced compared to the target tooth thickness. However, because such a reduced tooth thickness does not significantly affect the rolling behavior of the subsequent gear, since when the gear is used, usually only either the left or the right tooth flanks roll with the counter flanks of a counter gear, this effect can be tolerated and does not bring any real disadvantages.

In embodiments of the present invention, it is generally possible to determine a first and a second zero point shift for the left and right tooth flanks separately from one another. However, this would more often than actually necessary result in the tooth thickness of the finished tooth being thinner than the tooth thickness actually specified by the designer. In order to avoid this effect at least in cases where it is not necessary, further preferred embodiments are proposed in which a joint evaluation of right and left tooth flanks can first be carried out in order to determine a common rotary zero point shift. This then checks whether a positive value or a value greater than or equal to a specified allowance is achieved or can be achieved at all probe positions on the left and right tooth flanks. If this is not possible, a first and second zero point shift can be determined in the next step by separately evaluating the left and right tooth flanks.

Preferably, the plurality of sensing positions of a tooth flank are arranged on the tooth flank in rows that run in the tooth width direction and columns that run in the tooth height direction, wherein the measuring sensing means controlled by the machine control device preferably scans the sensing positions of a tooth flank column by column, preferably by sensing sensing positions of a column one after the other and, after scanning the sensing positions of the column, scanning the sensing positions of an adjacent column.

This has the advantage that the touch positions of a tooth flank can be distributed on this tooth flank in a particularly simple manner according to a regular point grid in rows and columns essentially over the entire width and the entire height of the tooth flank. Touch positions on a tooth flank can thus be arranged in a simple manner in such a way that the thermal distortion or the change in thermal distortion can be traced evenly distributed over essentially the entire tooth flank surface. Such a change in thermal distortion over the tooth flank surface is also strongly dependent on the respective gear type and the respective toothing shape, since the distortion typically increases with increasing distance from the base body and the tooth tip.

By scanning the scanning positions of a tooth flank column by column according to this preferred embodiment, the scanning process for the individual tooth flanks can also be carried out more efficiently and at a higher feed rate, since a line-by-line scanning, in contrast, particularly near the tooth base, where the tooth gap typically has a minimum thickness, would have to be carried out very carefully and slowly to avoid collisions, and in contrast, with column-by-column scanning the scanning process can therefore be carried out more efficiently at a faster feed rate.

Preferably, the measuring probe means scans the scanning positions of a column in the direction of the tooth base, preferably by scanning the scanning position closest to the tooth tip for each column first and scanning the scanning position closest to the tooth base last. Preferably, after scanning the scanning position of a column closest to the tooth base, the machine control device controls the scanning means in rapid traverse to the scanning position closest to the tooth tip of the adjacent column.

According to this preferred embodiment, the advantage of an even faster and more efficient scanning of the scanning positions of a tooth flank is achieved, since the slower feed rate when scanning the scanning positions of a gap is carried out towards the narrowing tooth base and the movement of the scanning means to the next scanning position of the adjacent gap can thus take place obliquely from the tooth base towards the tooth tip, as a result of which, due to the tooth gap thickness increasing towards the tooth tip, the movement to the adjacent gap can be carried out in efficient and fast but less precisely controllable rapid traverse, while at the same time reducing the risk of collisions. is significantly reduced compared to a process at an angle to the tooth base, where rapid traverse could not be used due to the tooth gap thickness becoming thinner towards the tooth base.

Preferably, the plurality of tooth flanks comprises a first tooth flank and a second tooth flank, wherein the first and second tooth flanks are preferably either both left tooth flanks or both right tooth flanks, and wherein the first tooth flank is preferably arranged on a first side of the gear, which is preferably substantially radially opposite a second side of the gear on which the second tooth flank is arranged, preferably with respect to the gear axis. Alternatively, the plurality of tooth flanks preferably comprises a group of N tooth flanks, wherein the N tooth flanks of the group are preferably either all left tooth flanks or all right tooth flanks, and wherein the N tooth flanks of the group are preferably arranged circumferentially of the gear with substantially the same angular distance between each other, i.e. preferably substantially at an angular distance of 360°/N. The previously described embodiment with respect to the first and second tooth flanks essentially corresponds to the special case N = 2.

As already described above, not only can a strong change in the thermal distortion occur for scanning positions on a tooth flank, which is to be compensated by the rotary zero point shift, but different thermal distortions can also occur for different tooth flanks. In order to be able to compensate for this better, this preferred embodiment not only provides for scanning several tooth flanks, but also for selecting the tooth flanks to be scanned so that they are distributed essentially evenly over the entire circumference of the gear as far as possible.

If two tooth flanks (preferably either left or right) are to be scanned, these are preferably selected essentially on opposite sides of the gear. In this case, "essentially" particularly preferably means that the tooth flanks do not necessarily have to be arranged exactly opposite each other, i.e. at 180°, but preferably within opposite angular segments that have an angle of less than or equal to 90°, preferably less than or equal to 45°.

If there are three or more (preferably either left or right) tooth flanks to be scanned, i.e. N > 2, these are preferably selected essentially at an angular distance of 360°/N from one another. In this case, "essentially" particularly preferably means that the N tooth flanks do not necessarily have to be arranged at an angular distance of 360°/N, but preferably each within angular segments that have an angular distance of 360°/N from one another and preferably have a respective angle of less than or equal to 180°/N, preferably less than or equal to 90°/N.

Preferably, the machine control device is configured to control the measuring probe for scanning the probe positions on the basis of probe data, wherein the probe data for each probe position preferably indicate a predetermined target position, a predetermined probe direction and/or a predetermined orientation direction for the measuring probe.

Here, the orientation direction for the measuring probe means refers to a specification of a direction to be taken by a longitudinal axis of the measuring probe means during the scanning process at the scanning position, e.g. when using a stylus with a probe ball arranged at the tip of the longitudinal axis of the stylus.

The target position specifies (preferably in the machine tool coordinate system) the position of a scanning target for the probe position and the probe direction preferably specifies a feed direction for the probe when scanning the probe position towards the target position.

Overall, a probe position is then preferably scanned on the basis of the probe data in such a way that the measuring probe is moved in a fixed orientation according to the specified orientation direction in the direction of the specified probe direction to the specified target position until a probe contact with the tooth flank is achieved at the probe position, at which the actual position can then be measured. The specified target position can, for example, correspond to the specified target position of the tooth flank (i.e. without distortion) or also to a position that is defined by the specified target position plus a predefined allowance amount of a specified allowance, e.g. in the direction of the surface normal of the target flank shape at the probe position.

Preferably, the touch data for all touch positions of a tooth flank indicate the same predetermined orientation direction for the measuring probe, so that the machine control device preferably controls the measuring probe in such a way that the orientation direction of the measuring probe remains unchanged during the scanning process of the touch positions of a tooth flank. Preferably, the at least 5 axes of the machine tool comprise at least two rotary axes, wherein the predetermined orientation direction of the touch data for a touch position preferably specifies a numerical position specification for the position to be assumed by the at least two rotary axes of the machine tool when scanning the tooth flank at the touch position.

This has the advantage that the accuracy when scanning the scanning positions of a tooth flank can be advantageously increased, since the specified scanning orientation and thus the maintained rotary axis position of the rotary axes is not changed during the scanning process of all scanning positions of a tooth flank. The scanning movements on a tooth flank are then only controlled by the linear axes of the machine tool with the rotary axes fixed, so that the actual scanning positions for the respective tooth flank can advantageously be recorded with greater relative accuracy to one another.

Preferably, the machine tool further comprises an input means via which a user can specify a respective plurality of touch positions for one or more tooth flanks, and/or an interface means via which touch position data can be entered which specify a respective plurality of touch positions for one or more tooth flanks. Preferably, the machine control device is then set up to automatically generate the touch data on the basis of the specified touch positions.

This has the advantage that a user of the machine tool can easily specify touch positions that are to be used as the basis for the alignment process, in that the touch positions can either be entered directly on the machine tool using the input device or can be transmitted to the machine tool's machine control device via the interface. The interface can include, for example, an Ethernet, LAN, WLAN and/or USB interface for inputting and outputting data on the machine tool. The user can advantageously only specify the respective target positions, whereby the other required touch data can be generated automatically on the machine tool by the machine control device.

Preferably, the respective specified scanning direction for each scanning position on a tooth flank is aligned parallel to a normal vector that is perpendicular to the respective scanning position on the tooth flank. The scanning direction can thus be easily calculated on the basis of the target flank geometry and the target positions, since the scanning direction is based on the surface normal of the target flank at the scanning position. In addition, the actual scanning process can be carried out more precisely at a scanning position. The scanning process can be achieved most precisely by scanning the actual flank perpendicularly, whereby the exact perpendicular direction to the actual flank at the scanning position is not exactly known due to the unknown distortion. By using the surface normal to the target flank surface at the scanning position to align the scanning direction, the accuracy of the scanning can be advantageously optimized in a simple manner on average across all scanning positions, even without knowledge of the real surface normal of the flank shape with distortion.

Preferably, the machine control device is set up to determine the at least one rotary zero point shift of the gearwheel clamped to the clamping means under the condition that material is removed at each touch position during final machining of the gearwheel. This can be made possible in a simple manner by checking the determined rotary zero point shift, for example for all determined target-actual deviations, in order to find out whether the determined zero point shift is not sufficient at one or more of the touch positions to remove material at this touch position during final machining. On the basis of this check, the determined zero point shift can then be slightly corrected if necessary in order to be able to remove material at these touch positions as well, whereby it should preferably be checked again whether this correction could not lead to no material being removed at other touch positions. By determining a zero point shift or corrected zero point shift, in which material is removed at all touch positions during final machining, it can be better avoided in particular that there are any places on tooth flanks where no material is removed.

In a similar way, as described below, it is also possible to specify a minimum material removal depth during finishing for determining the rotary zero point shift. This can be specified again by a user via an input device or in data form via a data interface.

Preferably, the machine control device is designed to determine the at least one rotational zero point shift of the gearwheel clamped to the clamping means, taking into account a predetermined minimum material removal depth, with the proviso that during final machining of the gearwheel, at least material up to the predetermined minimum material removal depth is removed at each touch position.

Preferably, the machine control device comprises a storage means and is designed to store the at least one determined rotary zero point shift for the clamped gear. This has the advantage that the stored rotary zero point shift can be easily taken into account numerically during the subsequent final machining, since the stored value can always be used again even during the processing of the control data when the final machining is carried out.

According to a second aspect of the invention, a method is proposed for controlling an automatic rotary alignment process for determining a rotary zero point shift for finishing a gear on a numerically controlled machine tool, wherein the machine tool is preferably designed according to one or more of the embodiments described above or the alignment process is carried out as on a machine tool according to one or more of the embodiments described above.

According to the invention, the method comprises determining a respective actual position at a plurality of predetermined probe positions on each tooth flank of a plurality of tooth flanks of the gear by means of a measuring probe, comparing the determined actual position for each of the predetermined probe positions with a respective predetermined target position, determining a target-actual deviation based on the comparison for each probe position, and determining at least one rotary zero point shift for the final machining of the gear clamped to the clamping means based on the determined target-actual deviations.

Preferably, the final machining of the clamped gear controlled by the machine control device follows automatically after the automatic alignment process on the basis of control data specified for the final machining, wherein the at least one determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the gear.

According to the invention, the plurality of tooth flanks comprise a group of left tooth flanks and a group of right tooth flanks, wherein the target-actual deviations determined for the group of left tooth flanks and the target-actual deviations determined for the group of right tooth flanks are evaluated separately. Preferably, in the step of determining at least one rotary zero point shift, a first zero point shift for the group of left tooth flanks and a second zero point shift for the group of right tooth flanks are determined.

Preferably, the final machining of the clamped gear controlled by the machine control device on the basis of control data specified for the final machining automatically follows the automatic alignment process, wherein the first determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the left tooth flanks and the second determined rotary zero point shift is preferably automatically taken into account when controlling the final machining of the right tooth flanks.

Preferably, the plurality of sensing positions of a tooth flank are arranged on the tooth flank in rows which run in the tooth width direction and columns which run in the tooth height direction, wherein in the step of determining the respective actual positions the measuring sensing means preferably scans the sensing positions of a tooth flank column by column by sensing sensing positions of a column one after the other and, after scanning the sensing positions of the column, the sensing positions of an adjacent column are scanned.

Preferably, the measuring probe means scans the scanning positions of a column in the direction of the tooth base, whereby for each column the scanning position closest to the tooth tip is scanned first and the scanning position closest to the tooth base is scanned last. Preferably, after scanning the scanning position of a column closest to the tooth base, the probe means is controlled in rapid traverse to the scanning position of the adjacent column closest to the tooth tip.

Preferably, the plurality of tooth flanks comprise a first tooth flank and a second tooth flank, wherein the first and second tooth flanks are preferably either both left tooth flanks or both right tooth flanks, and wherein the first tooth flank is preferably arranged on a first side of the gear that is substantially radially opposite a second side of the gear on which the second tooth flank is arranged with respect to the gear axis. Alternatively, the plurality of tooth flanks preferably comprise a group of N tooth flanks, wherein the N tooth flanks of the group are preferably either all left tooth flanks or all right tooth flanks, and wherein the N tooth flanks of the group are preferably arranged circumferentially of the gear with a substantially constant angular distance between each other.

Preferably, the measuring probe means for scanning the scanning positions is controlled on the basis of scanning data, wherein the scanning data preferably indicate a predetermined target position, a predetermined scanning direction and/or a predetermined orientation direction for the measuring probe means for each scanning position. Preferably, the scanning data indicate the same predetermined orientation direction for the measuring probe means for all scanning positions of a tooth flank, so that the measuring probe means is preferably controlled in such a way that the orientation direction of the measuring probe means remains unchanged during the scanning process of the scanning positions of a tooth flank.

Preferably, the at least 5 axes of the machine tool comprise at least two rotary axes, wherein the predetermined orientation direction of the scanning data for a scanning position preferably indicates a position specification for the at least two rotary axes of the machine tool when scanning the tooth flank at the scanning position.

Preferably, the touch data are generated automatically on the basis of predetermined touch positions, wherein the predetermined touch positions can preferably be specified by a user via an input means and/or via an interface means for one or more tooth flanks.

Preferably, the respective predetermined scanning direction for each scanning position on a tooth flank is aligned parallel to a normal vector which is perpendicular to the respective scanning position on the tooth flank.

Preferably, the at least one rotary zero point shift of the gearwheel clamped to the clamping means is determined with the proviso that material is removed at each touch position during final machining of the gearwheel. Preferably, the at least one rotary zero point shift of the gearwheel clamped to the clamping means is determined taking into account a predetermined minimum material removal depth, with the proviso that material is removed at least up to the predetermined minimum material removal depth during final machining of the gearwheel at each touch position.

Preferably, the at least one determined rotational zero point shift for the clamped gear is stored in a storage means.

According to a third aspect, a computer program product is proposed which comprises a computer-readable medium and a computer program stored therein, wherein the computer program is stored in the form of a sequence of states corresponding to commands which are configured to be processed by a machine control device of a numerically controlled machine tool according to one or more of the embodiments described above, so that the machine control device controls a method according to one or more of the embodiments described above on the machine tool on the basis of the commands.

In summary, in view of the problems of the alignment methods known from the prior art that have already been described above and occur in connection with an alignment process for determining a rotary zero point shift, the present invention makes it possible to provide an improved alignment process for soft-machined and heat-treated gears on a machine tool, in which the disadvantages described above can be avoided and in which the rotary zero point shift can still produce advantageous results, particularly in the case of very large gears with diameters of up to over a meter or more, so that during the final machining it can be avoided that points occur on tooth flanks where too much and/or too little material is removed.

Short description of the attached figures

• 1 shows an example of a schematic representation of a machine tool according to an embodiment of the invention.
• 2 shows an example of a schematic representation of two adjacent teeth of a straight-toothed spur gear in perspective.
• 3 shows an example of a schematic representation of a right tooth flank to illustrate a scanning process on a tooth flank according to an embodiment of the invention.
• 4 shows an example of a schematic representation of actual positions and target positions of a column of probe positions on tooth flanks of a tooth from 2 .
• 5 shows an exemplary flow chart of an alignment process for finishing a gear according to an embodiment of the present invention.

Detailed description of the attached figures and preferred embodiments

In the following, exemplary preferred embodiments of the present invention are The invention is described in detail with reference to the accompanying figures. However, the present invention is not limited to the embodiments described. The present invention is defined by the scope of the patent claims. Identical or similar features of the embodiments are identified in the figures with the same reference numerals.

1 shows, by way of example, a schematic representation of a machine tool 100 according to an embodiment of the invention. The machine tool 100 is a numerically controlled machine tool with at least 5 axes for machining a workpiece 200 clamped to a clamping means 130 of the machine tool 100 by means of a tool held on a work spindle 111 of the machine tool 100.

The machine tool 100 comprises three linear axes X, Y, and Z (not shown) and two rotary axes, e.g. a first rotary axis A, B or a combination of A and B (not shown) and a second rotary axis C (around rotation axis M1 in 1 ), by means of which the tool held on the work spindle 111 can be controlled relative to the workpiece 200 clamped on the clamping means 120, in particular in three translational degrees of freedom and two rotational degrees of freedom. To control the axis movements of the three linear axes X, Y, and Z and the two rotary axes, the machine tool comprises a numerical machine control device 150, which preferably has a CNC control device and a PLC control device, wherein the machine control device 150 is set up to control the tool held on the work spindle 111 of the machine tool 100 relative to the workpiece 200 clamped on the clamping means 130 of the machine tool 100 on the basis of numerical control data, in particular for example on the basis of one or more NC programs.

The work spindle 111 is held on a spindle head 110 of the machine tool, which can be driven in rotation via a rotary axis (not shown), and is designed to hold one or more tools on a tool holder interface. Furthermore, the work spindle 111 is designed to drive a tool held on the tool holder, such as a milling or drilling tool, in rotation to generate the cutting movement when machining a workpiece on the machine tool at high speed (tool-carrying spindle). In addition to cutting tools, it is also possible to hold non-cutting tools on the work spindle 111 and to move them by means of the at least 5 axes relative to the workpiece 200 clamped on the clamping means 130. The 1 The tool shown is, for example, a measuring probe tool 140 (e.g. measuring probe or stylus) by means of which the clamped workpiece 200 can be scanned at a scanning position to determine the position of the workpiece surface.

The machine tool further comprises a rotary table 120 on which the clamping means 130 for clamping a workpiece 200 is mounted and which can be rotated about the rotation axis M1 by means of the rotary axis B in 1 is controllable.

In this exemplary embodiment, the machine control device 150 comprises, for example, an interface 170 for the input and output of control data such as NC data comprising one or more NC programs. The interface 170 can have a wide variety of data interfaces, e.g. a LAN interface, a WLAN interface, an Ethernet interface, a Bluetooth interface, a USB interface, etc.

The machine control device 150 also includes an operating device 160, via which an operator can operate the machine tool 100 and in particular the machine control device 150. In this exemplary embodiment, the operating device 160 includes a display unit 161 for displaying a graphical user interface (comprising means for visually transmitting information, i.e., for example, a monitor, touchscreen or screen, or also bar displays, lamps, LEDs, etc.) and operating units 162a and 162b for manually entering operating commands. For example, the operating unit 162a can be designed with a keyboard and/or softkeys, and the operating unit 162b can be designed, for example, as a position-indicating operating unit, e.g. as a computer mouse, a tracking ball, a touchpad, a joystick or the like.

According to the present invention, the machine tool 100 is according to 1 designed to control an automatic rotary alignment process for determining a rotary zero point shift for a final machining of a gear 200 clamped to the clamping means 130. By way of example, the gear 200 is in 1 as a straight-toothed bevel gear. However, the present invention is advantageously applicable for carrying out an automatic rotary alignment process for determining a rotary zero point shift for finishing a wide variety of gears (e.g. spur gears, bevel gears, ring gears, etc.) with any toothing form (e.g. straight-toothed, helical gears, curved gears, spiral gears, etc.) and also with any gear profiles (e.g. involute profile, cycloid profile, etc.). Here, the machining, in particular milling, as well as the control of the probing process in the sense of the invention for bevel gears is carried out on 5 axes (ie by controlling at least three linear axes and at least two rotary axes), but the machining, in particular milling, as well as the control of the probing process in the sense of the invention for spur gears can also be carried out on 4 axes (ie by controlling at least three linear axes and at least one rotary axis).

In this automatic rotary alignment process, the measuring probe 140, which is controlled by the machine control device 150 and mounted on the work spindle 111, determines or measures a respective actual position for a plurality of predetermined tooth flanks of the gear 200 at a plurality of predetermined probe positions on each of the predetermined tooth flanks. The machine control device 150 then compares the determined actual position with a respective predetermined target position for each of the predetermined probe positions and determines or calculates a target-actual deviation for each probe position on the basis of this comparison. The machine control device 150 then automatically determines or calculates at least one rotary zero point shift for the final machining of the gear 200 clamped on the clamping means 130 on the basis of the determined target-actual deviations. This will be described in more detail later.

Preferably, the determined actual positions are stored together with the target positions and the associated target-actual deviations in a storage means of the machine control device 150. Furthermore, the determined rotary zero point shift for the final machining is preferably also stored in the storage means in order to be taken into account in the subsequent final machining.

2 shows an example of a schematic representation of two adjacent teeth 201 and 202 of a straight-toothed spur gear in perspective. The direction arrows ZH, ZB, and ZD in 2 indicate the directions ZH in the direction of the tooth height (tooth height direction), ZB in the direction of the tooth width (tooth width direction) and ZD in the direction of the tooth thickness (tooth thickness direction). The tooth 201 has a left tooth flank 201a and a right tooth flank 201b, and the tooth 202 also has a left tooth flank 202a and a right tooth flank 202b. Between the teeth 201 and 202, the gear has a tooth gap with the tooth base 203.

3 shows, by way of example, a schematic representation of the right tooth flank 201b to illustrate a scanning process on the tooth flank 201b according to an embodiment of the invention. The scanning process according to this embodiment is controlled on the basis of scanning data from the machine control device 150. It should be noted here that the present invention provides for a plurality of tooth flanks to be scanned. 3 illustrates the scanning process on only one tooth flank, and it is intended to carry out such a scanning process according to 3 successively on a plurality of tooth flanks of the gear.

According to an embodiment of the invention, it is particularly preferred that the plurality of tooth flanks to be scanned comprise a group of left tooth flanks and a group of right tooth flanks. Preferably, the number of left tooth flanks to be scanned and the number of right tooth flanks to be scanned are the same. In order to advantageously enable short travel paths during the entire scanning process, for example, the left and right tooth flanks of the same tooth can preferably be scanned, or even more expediently the left and right tooth flanks of the same tooth gap.

The sensing data preferably initially indicate the tooth flanks to be scanned, or at least the teeth or tooth gaps to be scanned, with the left and right tooth flanks then preferably being scanned for each specified tooth or tooth gap. For a tooth flank (or simultaneously for all right and/or left tooth flanks to be scanned), the sensing data also indicate a plurality of predetermined sensing positions for the scanning process. The machine control device 150 is set up to control the measuring probe 140 accommodated on the work spindle 111 to scan a plurality of sensing positions arranged on the tooth flank on the basis of the sensing data, with the sensing data indicating a predetermined target position, a predetermined sensing direction and a predetermined orientation direction TO for the measuring probe 140 for each sensing position x(i,j).

According to this embodiment, scanning positions x(i,j) are arranged in a grid on the tooth flank 201b to be scanned at the respective intersection points of grid rows L1, L2, L3 and L4, which run in the tooth width direction ZB on the tooth flank, and grid columns S1, S2, S3, S4, S5 and S6, which run in the tooth height direction ZH on the tooth flank. Here, the index i describes the row number by way of example and the index j describes the column number by way of example. Consequently, in this Example in 3 24 touch positions x(1,1), x(1,2), ..., x(4,5), x(4,6) are arranged on the tooth flank, wherein the respective actual position at the 24 touch positions is to be sensed using the measuring probe 140. Here and also in the following, the number of rows and columns or the number of predetermined touch positions is chosen merely as an example. The touch positions are preferably arranged in such a way that all touch positions are arranged on the tooth flank surface that will later be actively geared. This arrangement of the touch positions on a tooth flank in a grid in rows and columns merely represents a particularly expedient embodiment of the invention. In further embodiments of the invention, it is possible for the user to specify one or more freely selected touch positions for one or more of the tooth flanks.

According to this exemplary embodiment, the orientation direction TO for the measuring probe 140, which is also specified in the scanning data, designates a specification of a direction to be taken by a longitudinal axis of the measuring probe 140 during the scanning process of the 24 scanning positions of the tooth flank 201b. 3 shows, by way of example, a tip of the measuring probe 140 with a stylus 140b, at the end of which a probe ball 140a is attached, which is to be brought into contact with the tooth flank surface in order to scan the surface of the tooth flank 201b in order to determine an actual position at the probe positions x(i,j).

The target positions for each of the probe positions further specified in the probe data indicate (preferably in the machine tool coordinate system) the respective position of a scanning target for the respective probe position, and the probe directions further specified in the probe data indicate a respective feed direction for the measuring probe 140 when scanning the respective probe position to the respective target position. Thus, scanning is carried out at a specific probe position using the measuring probe 140 in such a way that the measuring probe 140 is oriented in accordance with the predetermined orientation direction TO (ie longitudinal axis of the stylus 140b in 3 aligned parallel to the orientation direction TO specified in the touch data) in front of the tooth flank such that the center of the measuring ball 140a lies on a straight line which intersects the touch position or the target position specified in the touch data and whose direction is specified by the normal vector on the tooth flank surface at the touch position or at the target position specified by the touch data.

After such positioning, the measuring probe 140 is controlled only by controlling one or more linear axes and with the rotary axes held in place such that the measuring ball 140a is moved towards the tooth flank in the scanning direction specified in the scanning data, which is aligned parallel to the direction of the normal vector on the tooth flank surface at the scanning position or at the target position specified by the scanning data, i.e. in the direction of the target position specified in the scanning data, until it is determined that the scanning ball 140 comes into contact with the tooth flank 201b at the scanning position. This contact position is recorded and is used to determine the actual position of the tooth flank at this respective scanning position. This process is repeated for all 24 scanning positions x(i,j) until the respective actual position has been determined for the tooth flank 201b for each scanning position x(i,j).

A particularly useful design of the scanning movement is indicated by the dashed arrows in 3 Here, the scanning positions are scanned column by column, starting with one of the two outer columns, in the direction of the tooth base (ie opposite to the tooth height direction ZH), whereby the scanning positions of a column j are scanned one after the other in the order x(1,j), x(2,j), x(3,j) and x(4,j).

After scanning the scanning position x(4,j) of column j closest to the tooth base 203 (e.g. arrows t1 and t2 from x(3,3) to x(4,3) in 3 ) the measuring probe 140 is moved for the next scanning step from the scanning position x(4,j) in rapid traverse to the scanning position x(1,j+1) closest to the tooth tip of the column j+1 adjacent to column j (e.g. arrow t3 from x(4,3) in the direction of x(1,4) in 3 ). The measuring probe is moved to the next column at rapid traverse, with the direction of movement away from the narrow tooth base, so that such a scanning process can be carried out quickly, accurately and efficiently with a significantly reduced risk of collision.

In the scanning process, the target position and the scanning direction (which is aligned parallel to the respective normal vector) in the scanning data change for each scanning position x(i,j), but the scanning data are particularly expediently generated or specified in such a way that the specified orientation direction TO is maintained when scanning all 24 scanning positions of the tooth flank by the stylus 140, i.e. that the rotary axes of the machine tool are held in place during the travel movements during the scanning process of the entire tooth flank 201b. This particularly advantageously increases the achievable relative accuracy of the actual position determinations at the scanning positions of the tooth flank 201b. The orientation direction TO is to be specified here under the proviso that no collisions occur during the scanning process (if necessary by means of a preceding virtual collision simulation). This is typically possible for almost all toothing forms and only for gears with very strong twist. of the flanks (e.g. in the case of bevel gears with very strongly curved arc or spiral teeth), it may be necessary to vary the orientation once or several times during the scanning process in order to avoid possible collisions.

The keying process is then carried out according to 3 for all predetermined left and right tooth flanks until the actual positions at each of the predetermined probe positions of the plurality of predetermined tooth flanks have been determined by means of the measuring probe 140. According to the invention, after determining the actual positions, a target-actual comparison is carried out for each probe position. Such a target-actual comparison is exemplary for probe positions of a column of a left and a right tooth flank of a tooth in 4 illustrated.

Typically, the information on the tactile data refers to a coordinate system in which one of the main axes of the machine tool (usually the Z axis) lies exactly on the center axis of the workpiece or in which the center axis of the workpiece is exactly aligned with the rotation axis M1 of the rotary table 120. In the previously described tactile process on the machine tool, however, the workpiece 200 can also be clamped in any way in the clamping means 130 in further embodiments, e.g. by aligning the center axis of the workpiece 200 axially parallel but offset to the rotation axis M1 of the rotary table 120.

In such embodiments, such a clamping deviation between the rotation center of the rotary axis B of the machine tool and the center axis of the workpiece 200 can be automatically compensated by the machine control device 150 by means of a coordinate conversion or coordinate transformation, i.e. the touch data or the position and direction information in the touch data can be subjected to an automatic coordinate transformation in order to automatically compensate for a clamping deviation between the rotation center of the rotary axis B of the machine tool and the center axis of the workpiece 200. Analogously, the target positions can be subjected to an automatic coordinate transformation and/or the actual positions determined in the touch process can be subjected to an inverse transformation.

4 shows an example of a schematic representation of actual positions and target positions of a column of probe positions on tooth flanks 201a (left tooth flank) and 201b (right tooth flank) of tooth 201 from 2 or the tooth flank 201b from 3 column S6 (essentially in the profile section through tooth 201).

The dashed lines in 4 correspond to the nominal profile of the tooth flanks 201a and 201b, marked as 201a _NOMINAL and 201b _NOMINAL along column S6 from 3 The target profile of the tooth flanks or the required target positions of the tooth flank at the touch positions can be determined, for example, on the basis of a numerical virtual model of the gear geometry after a previous soft machining on the machine tool, e.g. on the basis of a CAD model of the soft-machined gear, whereby the virtual model of the gear may have been used as the basis for generating the numerical control data for the soft machining. In this case, an allowance specified by the operator can also be taken into account for the target profile of the tooth flanks.

The following is an example of the course of columns S6 in 4 exactly the profile section, so that, for example, the columns S6 of the left and right flanks both lie in a profile section plane. However, this is only for illustration purposes and in general it is not necessary for a column of probe positions on a tooth flank to lie exactly in a profile section plane of the respective tooth. Likewise, it is not necessary for the columns of a left and a right tooth flank to lie in a common plane. The arrangement of the probe data of the left and right tooth flanks can also be specified completely independently of each other.

In 4 the respective touch positions of the left flank 201a _TARGET are designated x(1,6,L) to x(4,6,L) and the respective touch positions of the right flank 201b _TARGET are designated x(1,6,R) to x(4,6,R). A further index k has been added so that x(i,j,k) now designates exactly the respective touch point with i = 1, ... , N _z , where N _Z indicates the number of rows per tooth flank, j = 1, ... , N _S , where N _S indicates the number of columns per tooth flank, and k = R, L with R for a right tooth flank and L for a left tooth flank. The number of rows and columns on the right and left tooth flanks is assumed to be the same, but these can also be different, so that the number of touch positions on the left tooth flanks and the number of touch positions on the right tooth flanks can be different.

The continuous lines in 4 correspond to the actual profile of the tooth flanks 201a and 201b, marked as 201a _IST and 201b _IST along column S6 from 3 . In this case, 4 It is assumed that the actual profile of the tooth flanks deviates from the desired profile of the tooth flanks due to a distortion of the tooth flanks resulting from a previous hardening heat treatment after soft machining of the gear. At the respective key positions, according to 3 the actual positions are determined using the measuring probe 140. The respective determined actual positions at the respective probe positions are identified by y(i,j,k) as an example, where the indices i, j and k indicate the row number i and the column number j analogously to the indices of the target positions x(i,j,k), and whether the flank is a right flank (k = R) or a left flank (k=L). However, since the actual positions y(i,j,k) are determined according to 3 For example, if the scanning is carried out in a scanning direction corresponding to the respective normal vector on the respective tooth flank (according to the target curve 201a _TARGET or 201b _TARGET ) at the scanning position, the determined actual positions y(i,j,k) are essentially positioned in the respective normal direction of the target positions x(i,j,k).

By comparing the respective target positions x(i,j,k) and the determined actual positions y(i,j,k), the corresponding target-actual deviation parameters Δ(i,j,k) can be determined in a next step. These target-actual deviation parameters Δ(i,j,k) are preferably calculated as the amount of the distance between the respective target and actual positions x(i,j,k) and y(i,j,k) with a prefix that indicates whether the tooth flank is warped towards or away from the tooth (distortion direction).

Here, the target-actual deviation parameters Δ(i,j,k) can take on both positive and negative values, whereby a positive sign indicates, for example, that the tooth flank is warped away from the tooth at the respective probe position, and a negative sign indicates, for example, that the tooth flank is warped towards the tooth at the respective probe position. In this case, for example, the parameter values for Δ(1,6,L) to Δ(4,6,L) as well as Δ(3,6,R) and Δ(4,6,R) in 4 positive and Δ(1,6,R) would be negative; Δ(2,6,R) would be zero, for example, since the target and actual positions x(2,6,R) and y(2,6,R) in 4 are, for example, congruent or identical (locally no distortion at the probe position i = 2, j = 6 and k = R).

In order to further optimize the determination of the rotary zero point shift, according to an embodiment of the invention it is further provided to scan a plurality of left and right tooth flanks at different locations on the gear. In particular, N pairs of right and left tooth flanks can be scanned at different locations on the gear. It is conceivable, for example, that for a plurality of predetermined teeth or tooth gaps at different locations on the gear, the right and left tooth flanks are scanned as described above. Here, the probe positions can be further specified with an additional index m with target positions x(m,i,j,k), actual positions y(m,i,j,k) and target-actual deviations Δ(m,i,j,k), where m = 1, ... N indicates the respective tooth or tooth gap to be scanned (where N corresponds to the number of specified teeth or tooth gaps to be scanned) and the indices i, j and k indicate the respective row and column for each of these teeth or tooth gaps, and whether the respective probe position is located on the left or right tooth flank.

If there are two teeth or tooth gaps to be scanned (m = 1, 2), these are preferably selected essentially on opposite sides of the gear. In this case, "essentially" particularly preferably means that the teeth or tooth gaps do not necessarily have to be arranged exactly opposite each other, i.e. at 180°, but preferably within opposite angular segments that have an angle of less than or equal to 90°, preferably less than or equal to 45°. If there are three or more teeth or tooth gaps to be scanned, i.e. m = 1, 2, ..., N with N > 2, these are preferably selected essentially at an angular distance of 360°/N from each other. Here, “substantially” particularly preferably means that the N teeth or tooth gaps do not necessarily have to be arranged at an angular distance of 360°/N, but preferably each within angular segments which have an angular distance of 360°/N from one another and preferably have a respective angle of less than or equal to 180°/N, preferably less than or equal to 90°/N.

After determining the respective target-actual deviations Δ(m,i,j,k) at the specified contact positions of the specified tooth flanks, a rotary zero point shift is determined on the basis of the determined target-actual deviations Δ(m,i,j,k). For this purpose, the determined target-actual deviations Δ(m,i,j,k) can be viewed as a function of the one-parametric rotary zero point shift, whereby the zero point shift of a positive or negative rotation of the gear around the rotation axis of the gear can be viewed, whereby the determined target-actual deviations Δ(m,i,j,k) correspond to the function values for a zero point shift equal to zero. By means of simulation calculations, the respective function values of the target-actual deviations can be varied as a function of the zero point shift in order to be able to determine an optimal rotary zero point shift by determining a fit value or best fit value using a mathematical compensation calculation. The zero point shift can be specified, for example, by an angle value θ (or by a position specification of the rotary axis B of the rotary table 120 in the machine tool coordinate system), whereby the target-actual deviations are specified as a function Δ(m,i,j,k)(θ) of the angle value θ can be simulated and the determined target-actual deviations represent the function values Δ(m,i,j,k)(0) at θ = 0.

To determine this fit value or best fit value, a distance value D(θ) can preferably be calculated on the basis of the determined target-actual deviations, whereby the distance value D(θ) preferably represents a value describing the size of the total deviation taking into account all determined target-actual deviations. In the mathematical compensation process, this distance value is then automatically minimized, preferably by varying the rotary zero point shift θ, and the value of the rotary zero point shift with the distance value minimized then results in the determined optimized rotary zero point shift for use in the subsequent final machining of the gear within the framework of this mathematical compensation calculation.

Since the target-actual deviations can in turn be defined as functions depending on the zero point shift θ, this defined distance value D(θ) can be viewed as a function of the zero point shift θ and minimized by simulated variation of the zero point shift θ in order to determine the optimized rotary zero point shift, which should then be used as the basis for the final machining of the clamped gear on the basis of the numerical control data for the final machining.

It should be noted that the values of the individual target-actual deviations can take on both positive and negative values. For this reason, the distance value based on the target-actual deviations should preferably be selected in such a way that it can be described as a function of the amounts of the target-actual deviations or, preferably, as a function of the squares of the target-actual deviations.

The distance value can, for example, be selected on the basis of the target-actual deviations, preferably in such a way that the value of the distance value increases strictly monotonically with the amount of each individual target-actual deviation or preferably with the square of each individual target-actual deviation. The distance value could expediently be defined as a strictly monotonically increasing function of the sum of the amounts of all target-actual deviations (e.g. D(θ) = Σ|Δ(m,i,j,k)(θ)| for all probe positions, ie all m, i, j, and k) or preferably as a strictly monotonically increasing function of the sum of the squares of all target-actual deviations (e.g. D(θ) = Σ[Δ(m,i,j,k)(θ)] ² or also D(θ) = sqrt(Σ[Δ(m,i,j,k)(θ)] ² ), ie as the square root of the sum of all squares of the individual target-actual deviations, for all probe positions, ie all m, i, j, and k). As already mentioned, an optimized zero point shift can then be determined in a mathematical compensation process by minimizing the distance value D(θ) with a simulated variation of the zero point shift θ.

In particularly preferred embodiments, in addition to or as an alternative to the joint evaluation, it is also possible to evaluate the left and right tooth flanks separately and to determine a separate optimized zero point shift for the right and left. In this case, two separate distance values D1(θ) and D2(θ) would then be defined, one for the right and one for the left tooth flanks, and these distance values would then be minimized separately from one another. Here, the distance values could be defined analogously to the joint evaluation as described above, but only evaluated for the left or right tooth flanks (e.g. D1(θ) = Σ|Δ(m,i,j,R)(θ)|, D1(θ) = Σ[Δ(m,i,j,R)(θ)] ² or also D(θ) = sqrt(Σ[Δ(m,i,j,R)(θ)] ² ) for all right probe positions, ie all m, i, and j with fixed k = R and D2(θ) = Σ|Δ(m,i,j,L)(θ)|, D2(θ) = Σ[Δ(m,i,j,L)(θ)] ² or also D2(θ) = sqrt(Σ[Δ(m,i,j,L)(θ)] ² ) for all left probe positions, ie all m, i, and j with fixed k = L). The distance values D1 and D2 can then be minimized separately so that two independent optimized zero point shifts for the right and left tooth flanks can be determined.

This has the advantage that the final machining of the gear can be further improved. If the determination of a single rotary zero point shift with a joint evaluation of the target-actual deviations of the left and right tooth flanks leads to a result in which, after final processing, there are areas with too much material removal and/or areas with too little or no material removal due to excessive and varying thermal distortion of the tooth flanks, this can be avoided by evaluating the left and right tooth flanks separately and determining the first zero point shift for the left tooth flanks and the second zero point shift for the right tooth flanks.

In further preferred embodiments, the determined zero point shift or the rotary zero point shifts for the left and right tooth flanks are automatically checked again in the machine control device 150. In this case, it is preferably checked for each touch position in a simulation process on the basis of the control data for the final machining and/or on the basis of a virtual model of the gear after final machining whether and/or how much material is removed at the touch position taking into account the determined zero point shift or the rotary zero point shifts for the left and right tooth flanks are removed during final machining. Depending on the criteria described below, it can be checked whether material is removed at the respective probe positions and/or whether a specified minimum material removal depth is maintained at the respective probe positions. According to the following criteria, the determined zero point shift can be corrected again (if necessary separately for the left and right tooth flanks) and checked again.

Preferably, the machine control device 150 is set up to determine the at least one rotary zero point shift of the gearwheel clamped to the clamping means under the condition that material is removed at each touch position during final machining of the gearwheel. This can be made possible in a simple manner by checking the determined rotary zero point shift, for example for all determined target-actual deviations, in order to find out whether the determined zero point shift is not sufficient at one or more of the touch positions to remove material at this touch position during final machining. On the basis of this check, the determined zero point shift can then be slightly corrected if necessary in order to be able to remove material at these touch positions as well, whereby it should preferably be checked again whether this correction could not lead to no material being removed at other touch positions. By determining a zero point shift or corrected zero point shift, in which material is removed at all probe positions during final machining, it can be better avoided that there are any places on tooth flanks where no material is removed.

In a similar way, as described below, it is also possible to specify a minimum material removal depth during finishing for determining the rotary zero point shift. This can be specified again by a user via an input device or in data form via a data interface.

Preferably, the machine control device is designed to determine the at least one rotational zero point shift of the gearwheel clamped to the clamping means, taking into account a predetermined minimum material removal depth, with the proviso that during final machining of the gearwheel, at least material up to the predetermined minimum material removal depth is removed at each touch position.

In the above embodiments, a mathematical compensation method for determining a rotary zero point shift or for determining two rotary zero point shifts for the left and right tooth flanks separately was described in detail. In alternative embodiments, it is also possible to determine one or two zero point shifts according to the invention without a mathematical compensation method.

To determine the rotary zero point shift, the rotary zero point shift can, for example, be determined or calculated in a simple manner according to a particularly useful example in such a way that in a simulation, by varying the rotary zero point shift, it is checked which rotary zero point shift θ is at least required to make all target-actual deviations Δ(m,i,j,k)(θ) greater than or equal to zero or which rotary zero point shifts θ ₁ and θ ₂ are required to make all target-actual deviations Δ(m,i,j,L)(θ ₁ ) and Δ(m,i,j,R)(θ ₂ ) greater than or equal to zero (the latter with separate evaluation of the left and right tooth flanks).

In particular, it is possible, for example, to determine in a particularly simple manner which zero point shift is required to make the smallest of the determined target-actual deviations greater than or equal to zero, and to record this value as the determined rotational zero point shift.

Optionally to the above aspects, it is preferably also possible to additionally specify a minimum allowance, wherein the rotary zero point shift can then be determined in such a way that in a simulation, by varying the rotary zero point shift, it is checked which rotary zero point shift is at least required to make all target-actual deviations greater than or equal to the specified minimum allowance. In particular, it is preferably possible, for example, to determine in a particularly simple manner which zero point shift is required to make the smallest of the determined target-actual deviations greater than or equal to the specified allowance, and to record this value as the determined rotary zero point shift.

In the above-described embodiments for determining the rotary zero point shift, it must be taken into account that a rotary zero point shift in the above-mentioned definition of the signs of the target-actual deviations reduces the target-actual deviations on right flanks, while increases the target-actual deviations on left flanks, or increases the target-actual deviations on right flanks, while reducing the target-actual deviations on left flanks. If it is not possible to adjust right and left tooth flanks using the same rotary zero point shift, further embodiments of the present invention provide for right and left flanks to be evaluated separately and separate rotary zero point shifts to be determined.

5 shows an exemplary flow chart of an alignment process for finishing a gear according to an embodiment of the present invention. In a step S1, the gear 200, which has previously been soft-machined and subjected to a hardening heat treatment, is clamped to the clamping means 130 of the machine tool. In a further step S2 (which can alternatively also be carried out before S1), touch data for a touch process of the gear 200 are specified. These can be specified either via the interface 170 or manually via the operating device 160, or touch positions can be specified via the interface 170 or manually via the operating device 160, with the further touch data being generated automatically on the basis of the touch positions and a virtual model of the gear 200. After specifying the touch data, the scanning process is carried out in the next step S3, in which all touch positions of the gear 200 are scanned by means of the measuring probe 140 in order to determine the corresponding actual positions at the respective touch positions.

After determining the respective actual positions at all specified probe positions, in the next step S4, the respective target-actual deviations are calculated for all probe positions on the basis of specified target positions and the determined actual positions, and in the following step S5, a zero point shift or two zero point shifts for the right and left tooth flanks are determined separately using a mathematical compensation calculation. Following step S5, the final machining of the gear 200 is automatically carried out on the machine tool 100 on the basis of numerical control data for the final machining, taking into account the rotary zero point shifts determined in step S5.

In summary, in view of the problems of the alignment methods known from the prior art that have already been described above and occur in connection with an alignment process for determining a rotary zero point shift, the present invention makes it possible to provide an improved alignment process for soft-machined and heat-treated gears on a machine tool, in which the disadvantages described above can be avoided and in which the rotary zero point shift can still produce advantageous results, particularly in the case of very large gears with diameters of up to over one meter, so that during finishing it can be avoided that points occur on tooth flanks where too much and/or too little material is removed.

Claims (14)

Numerically controlled machine tool with at least 5 axes for machining a workpiece (200) clamped to a clamping means (130) of the machine tool (100) by means of a tool received on a work spindle (111) of the machine tool (100), comprising: a numerical machine control device (150) which is designed to control the tool received on the work spindle (111) of the machine tool (100) relative to the workpiece (200) clamped to the clamping means (130) of the machine tool (100) on the basis of numerical control data, wherein the machine control device (150) is further designed to control an automatic rotary alignment process for determining at least one rotary zero point shift for final machining of a gear (200) clamped to the clamping means (130), in which: - a measuring probe controlled by the machine control device (150) (140) with a plurality of tooth flanks (201a, 201b; 202a, 202b) of the gear (200) at a plurality of predetermined touch positions on each of the tooth flanks, the plurality of tooth flanks comprising a group of left tooth flanks (201a, 202a) and a group of right tooth flanks (201b, 202b), - the machine control device (150) compares the determined actual position with a respective predetermined target position for each of the predetermined touch positions and determines a target-actual deviation for each touch position on the basis of the comparison, - the machine control device (150) determines at least one rotary zero point shift for the final machining of the gear (200) clamped on the clamping means (130) on the basis of the determined target-actual deviations, and - the machine control device (150) is set up to determine the at least one rotary zero point shift of the gear (200) clamped on the clamping means (130) clamped gear (200) taking into account a predetermined minimum material removal depth, with the proviso that during final machining of the gear wheel (200) at each touch position at least material is removed up to the predetermined minimum material removal depth, and if this is not possible, the machine control device (150) is set up to separately evaluate the target-actual deviations determined for the group of left tooth flanks (201a, 202a) and the target-actual deviations determined for the group of right tooth flanks (201b, 202b), and to determine a first zero point shift for the group of left tooth flanks (201a, 202a) and a second zero point shift for the group of right tooth flanks (201b, 202b). Machine tool according to Claim 1 , characterized in that the machine control device (150) is designed to automatically control the final machining of the clamped gear (200) after the automatic alignment process on the basis of control data predetermined for the final machining, wherein the at least one determined rotary zero point shift is automatically taken into account when controlling the final machining of the gear (200). Machine tool according to Claim 1 , characterized in that the machine control device (150) is set up to automatically control the finishing of the clamped gear (200) after the automatic alignment process on the basis of control data predetermined for the finishing, wherein the first determined rotary zero point shift is automatically taken into account when controlling the finishing of the left tooth flanks (201a, 202a) and the second determined rotary zero point shift is automatically taken into account when controlling the finishing of the right tooth flanks (201b, 202b). Machine tool according to one of the preceding claims, characterized in that the plurality of sensing positions of a tooth flank are arranged on the tooth flank in rows (L1-L4) which run in the tooth width direction (ZB) and columns (S1-S6) which run in the tooth height direction (ZH), wherein the measuring sensing means (140) controlled by the machine control device (150) scans the sensing positions of a tooth flank column by column by sensing sensing positions of a column one after the other and, after scanning the sensing positions of the column, scanning the sensing positions of an adjacent column. Machine tool according to Claim 4 , characterized in that the measuring probe means (140) scans the scanning positions of a column in the direction of the tooth base, in that for each column the scanning position closest to the tooth tip is scanned first and the scanning position closest to the tooth base is scanned last, wherein the machine control device (150) controls the scanning means, after scanning the scanning position closest to the tooth base of a column, in rapid traverse to the scanning position closest to the tooth tip of the adjacent column. Machine tool according to one of the preceding claims, characterized in that the plurality of tooth flanks comprises a first tooth flank and a second tooth flank, wherein the first and second tooth flanks are either both left tooth flanks (201a, 202a) or both right tooth flanks (201b, 202b), and wherein the first tooth flank is arranged on a first side of the gear which is substantially radially opposite a second side of the gear on which the second tooth flank is arranged with respect to the gear axis; or the plurality of tooth flanks comprises a group of N tooth flanks, wherein the N tooth flanks of the group are either all left tooth flanks or all right tooth flanks, and wherein the N tooth flanks of the group are arranged circumferentially of the gear with a substantially constant angular distance between each other. Machine tool according to one of the preceding claims, characterized in that the machine control device (150) is designed to control the measuring probe means (140) for scanning the probe positions on the basis of probe data, wherein the probe data specify a predetermined target position, a predetermined probe direction and a predetermined orientation direction for the measuring probe means (140) for each probe position. Machine tool according to Claim 7 , characterized in that the scanning data for all scanning positions of a tooth flank indicate the same predetermined orientation direction for the measuring scanning means (140), so that the machine control device (150) controls the measuring scanning means (140) in such a way that the orientation direction of the measuring scanning means (140) remains unchanged during the scanning process of the scanning positions of a tooth flank. Machine tool according to Claim 7 or 8th , characterized in that the at least 5 axes of the machine tool (100) comprise at least two rotary axes, wherein the predetermined The specified orientation direction of the probe data for a probe position specifies a position specification for at least two rotary axes of the machine tool when scanning the tooth flank at the probe position. Machine tool according to one of the Claims 7 until 9 , further characterized by an input means (160, 162a, 162b) via which a user can specify a respective plurality of touch positions for one or more tooth flanks, and/or an interface means (170) via which touch position data can be entered which specify a respective plurality of touch positions for one or more tooth flanks, wherein the machine control device (150) is set up to automatically generate the touch data on the basis of the predetermined touch positions. Machine tool according to one of the Claims 7 until 10 , characterized in that the respective predetermined scanning direction for each scanning position on a tooth flank is aligned parallel to a normal vector which is perpendicular to the respective scanning position on the tooth flank. Machine tool according to one of the preceding claims, characterized in that the machine control device (150) is designed to determine the at least one rotational zero point displacement of the gear wheel (200) clamped to the clamping means (130) under the proviso that material is removed at each touch position during final machining of the gear wheel (200). Method for controlling an automatic rotary alignment process for determining a rotary zero point shift for final machining of a gear (200) on a numerically controlled machine tool (100) according to at least one of the preceding claims, comprising: - determining (S3) a respective actual position at a plurality of predetermined probe positions on each tooth flank of a plurality of tooth flanks of the gear (200) by means of a measuring probe means (140), - comparing the determined actual position for each of the predetermined probe positions with a respective predetermined target position, - determining (S4) a target-actual deviation based on the comparison for each probe position, and - determining (S5) at least one rotary zero point shift for the final machining of the gear (200) clamped on the clamping means (130) based on the determined target-actual deviations. Computer program product comprising a computer-readable medium and a computer program stored therein, wherein the computer program is stored in the form of a sequence of states corresponding to commands configured to be processed by a machine control device (150) of a numerically controlled machine tool (100), such that the machine control device (150) can execute a method according to Claim 13 on the machine tool (100).

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